The 19-year-old won the Formula Renault Eurocup title in 2019 before moving up to F3 last year, taking the title in a nail-biting final race of the season at Mugello.
Piastri described himself as ”super excited” to be with the team.
”We had a very successful 2020 season and Prema has proven to be the team to beat once again in F2 this year, so I’m extremely happy to be moving into the championship with them.”
René Rosin, Prema’s Team Principal, said of Piastri: “Not only he is a talented racer with outstanding speed skills. He has a clear understanding of the complexities of today’s motorsports and he is extremely adaptable.
”Having witnessed his progress and success throughout the 2020 season, taking our relationship to the next step for the 2021 FIA Formula 2 Championship felt like the natural thing to do and we look forward to having him on-track right from Bahrain.”